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Pension and Other Postretirement Benefits - Additional Information (Detail)
$ in Millions
9 Months Ended
Sep. 30, 2019
USD ($)
Pension Benefits  
Defined Benefit Plan Disclosure [Line Items]  
Employer contributions $ 267
Other Pension Plan  
Defined Benefit Plan Disclosure [Line Items]  
Benefits paid 16
Other Benefits  
Defined Benefit Plan Disclosure [Line Items]  
Benefits paid $ 32